This invention relates to non-pneumatic tires having angularly oriented ribbed members and webs between ribs composed of resilient polyether urethane elastomeric materials. In particular, a urethane made of polyether polyols having two distinctly different molecular weights are used to make the urethane elastomer.
Urethanes have been used in the manufacture of solid tires useful for such applications as industrial tires, off-the-road tires, bicycles tires and the like. They have not been entirely satisfactory in such applications because such urethane solid tires do not have the proper cushioning and handling characteristics for a soft vehicle ride on such applications as passenger vehicles. Also, such solid tires suffer from internal heat build-up and subsequent degradation of the elastomer material in prolonged high speed service conditions or under rough terrain situations where the tire is being deformed.
Various polyurethane elastomers have been proposed for use on such solid tires, including those described in U.S. Pat. No. 3,798,200 and U.S. Pat. No. 3,963,681 both to Kaneko et al. In these two pieces of prior art it is proposed that polyether urethane elastomers can be utilized which are prepared from two prepolymers having differing molecular weights. In 3,963,681 it is disclosed that by using a flex life test such De Mattia it is determined that the preferred urethane elastomer is one prepared using a polyfunctional isocyanate and a polyether prepared using prepolymers having different average molecular weights. It is further disclosed that for polytetramethylene ether glycol the critical molecular weight is 4,500. One of the two polyethers used to make the invention must have a molecular weight above the 4,500 critical molecular weight and the other must be below this critical molecular weight in order to achieve the improved De Mattia flex life. U.S. Pat. No. 3,798,200 discloses a 4,000 critical molecular weight for polytetramethylene glycol ethers utilized in the urethane teaches that the average weight of the two polyethers must lie between 4,500 and 20,000 weight average molecular weight. It further teaches that one of the polyethers must lie below the critical molecular weight of 4,500 and the other be above such a critical molecular weight. In comparative Example 9, composition outside of the invention of the reference is described in which a 1,900 molecular weight polyether and an 850 molecular weight is blended 50:50, reacted with 2 mols of 2,4 tolylene diisocyanate and subsequently cured with methylene bis ortho-chloroaniline. Such a composition was found to have poor cut growth and flex crack resistance as measured by De Mattia flex testing.
Contrary to the teachings of 3,798,200, it has been quite unexpectedly found that a non-pneumatic tire utilizing a rib-and-web structure of this invention yields a non-pneumatic tire which can favorably compare with pneumatic tires for service life under both high speed, long duration test conditions and under very rough road conditions while still giving good ride and handling characteristics similar to a pneumatic tire. Such a device of the invention is superior to a pneumatic tire in that it cannot be punctured or damaged in the way a pneumatic can.
The non-pneumatic tire concept set forward in European patent publication number 159,888 which claimed convention priority from U.S. Pat. application No. 600,932 filed Apr. 16, 1984, introduced a configuration of tire which utilized an entirely new design approach to a high speed non-pneumatic tire having suitable ride characteristics for passenger tires. This design features the ability of the ribs and webs to provide a variable spring rate in the tires and enables it to deform locally when an obstacle is encountered on a rough road driving condition. These requirements are in addition to the common requirements which were encountered in previous generations of solid tires that the internal heat build-up be kept to a minimum and the flex life of the tire be long.
In view of the unique requirements of structure as a object of the invention to provide a urethane material which can endure both long duration, high speed conditions as well as the ability to locally deflect in rough terrain service. It is a further object to provide a non-pneumatic tire having good vehicle ride characteristics under a variety of road conditions. In order to achieve such results, it is necessary to recognize that dynamic modulus of the material is critically important as well as flex fatigue life and dynamic heat build-up properties (hysteresis). The recognition of the criticality of utilizing a urethane with two distinct molecular weight glycols with an organic diamine curative provided the balance in properties required for good vehicle ride characteristics as well as long life.